1. Field of the Invention
This invention relates to percussion tools or machines for driving nails, rivets or the like.
2. Prior Art
When driving driven elements, such as a nail and a rivet, into a hard material such as concrete, using a nailing machine, the driven element can not often be fully driven into the hard material with one strike or impact. It has therefore been proposed a percussion tool of the type in which a striking piston is continuously moved reciprocally along a cylinder to apply a plurality of impacts to the driven element. In this case, the striking stroke and return stroke of the striking piston alternates with each other. When the striking piston reaches the starting and terminal ends of the stroke or those positions near such stroke ends, the striking piston serves as a switching valve to switch air supply connections, so that compressed air is applied to upper and lower surfaces of the striking piston alternately, thereby reciprocally moving the striking piston continuously.
In the case where the operating stroke of the striking piston is long in the above conventional machine, a driven element sometimes fails to be driven into a hard material a length corresponding to the length of the stroke of the striking piston, particularly where the driven element has a long shank portion. As a result, the switching valve is not switched, so that the striking piston can not be returned.
In addition, in the case where a great impact is caused by the striking action, the housing of the machine is rebounded upwardly due to a reaction encountered, which is undesirable from the viewpoint of operator safety.
Therefore, in the conventional percussion tool, the operating stroke of the striking piston has to be short, and much time is required for driving along driven element. And besides, the operator has to support the tool and moves it in accordance with the amount of driving of the driven element. This is a considerable burden on the part of the operator.
Generally, conventional nailing machines are provided with a nail feed mechanism for automatically feed nails in response to the operation of a striking piston for driving nails. A conventional nail feed mechanism can not be used in the nailing machine of the repeatedly operating type in which the striking piston is reciprocally moved repeatedly to drive one nail. Therefore, in such nailing machines of the repeatedly operating type, there has been used a nail feed mechanism of the type in which the nails are fed manually. One such conventional nail feed mechanism of the manually-operative type is disclosed in Japanese Patent Publication No. 17663/1982. In this nail feed mechanism, a plurality of nails are received in radially-arranged holes in a rotary magazine, and the magazine is rotated by manually operating an operating handle engaged in a groove formed in the periphery of the magazine so as to bring each hole, holding the nail, into alignment with the axis of a striking driver, thus feeding each nail.
With the manually-operative nail feed mechanism, however, a considerable force is required to feed the nails, and both hands have to be used to effect such nail feed operation. Therefore, the hand holding the nailing machine must once be off the machine. This affects the efficiency of the nailing operation.
In addition, the nail feed mechanism employing the rotary magazine can not be charged with many nails, and that portion of the mechanism adjacent to a nail ejecting port is bulky, so that the point of a material into which the nail is to be driven can not be seen clearly. This affects the nailing operation.
To overcome the above difficulties, it is considered to operate the nail feed mechanism, provided with a piston and cylinder device which is driven by compressed air as is the case with the conventional nailing machine, through a manually-operative valve. In this case, however, the nail feed mechanism may be inadvertently operated twice, in which instance two nails are fed to the nail ejecting portion and jammed therein, which adversely affects the nailing operation and may damage the nail ejecting portion and the striking driver.